Method and apparatus for cryogenic crystallization of fats

ABSTRACT

A method and apparatus for converting liquid fats into solid particles for blending with dry feed ingredients comprises spraying atomized liquid fat into the upper portion of the mixing chamber while directing a plurality of fine jets of liquid nitrogen against the liquid fat spray so as to produce solid fat particles which fall into the dry ingredients at the bottom of the mixing chamber. A homogeneous mix free of fat lumps is thereby readily obtained, even at the higher percentages of fat required for some animal feed.

The invention relates to a method and apparatus for converting liquidfats, oils or tallows into microcrystalline powders useful in thecompounding of dry animal feeds and in other applications in the foodindustry. In the following description and claims, the term "liquid fat"will be used generically to include liquid or molten fats, oils ortallows.

In order to induce upper growth and fattening of livestock, it isdesirable to add fats to the animal feed. In the raising of veal, a 20%level of added fat is typically employed. For this purpose, it is commoncommercial practice in the feed industry to spray liquid fat directlyinto the blender in which dry feed ingredients are mixed. A variety ofspray nozzles arranged in different configurations are employed to sprayor spread the liquid fat over the greatest possible surface area in themixing blender, with the aim of making a homogeneous mix through whichthe fat is uniformly dispersed.

Even at levels of added liquid fat of as low as 5%-10%, however, mixingproblems can develop. Non-uniformity in the mixing of liquid fat cangive rise to lumps containing higher concentrations of fats, which mustbe isolated from the rest of the batch for disposal or remixing; eithercorrective measure is wasteful and/or time consuming. Dry feedingredients can only absorb a certain percentage by weight of addedliquid fat before becoming "wet" (saturated), whereupon the texture ofthe mix changes from dry and powdery to wet and plastic. Saturation byfat during the mixing process is extremely undesirable, as it usuallyrequires the entire batch of feed to be scrapped.

Accordingly, where the feed or food product formula calls for a mixincluding a high percentage of fat, near or above the point where theaddition of sprayed liquid fat would cause saturation, the practice hasbeen to add predried powdered fats in bag form to the mixture. Knownsuch products are variously prepared by the cooling and flaking ofliquid films of fat, or by spraying hot liquid fat into a tower againstrefrigerated or cooled air causing the fat to solidify into a powder.The purchase of fifty-pound bags of powdered fat is quite costly,however, and the mixing of powdered fats with feed is both labourintensive and time consuming, as the bagged powdered fat must be addedmanually into the blender.

The present invention is based on the discovery that the conversion ofliquid fat to a crystallized or powdered form in situ, by spraying fatand a cryogenic liquid coolant such as liquid nitrogen or carbon dioxidetogether into the mixer, produces a homogeneous mix free of fat lumps,even at the higher fat percentages required for some animal feeds.

Crystallizing the fat in the blender itself has the substantialpractical advantage of eliminating the need for costly heat driedpre-bagged powdered fats and absorbing agents. The consistent productionof a dry batch of feed mix not only avoids waste, but reduces the labourand time which had previously been required for clean-up of mix stickingto the walls of the blender. Quality control is also improved over theliquid spray addition process, since a more uniform batch can beconsistently achieved. Further, the direct introduction of cryogenicallysolidified liquid fat particles has the effect of lowering the overalltemperature of the batch, thereby partially offsetting the heatgenerated by the friction of the blending process.

With a view to achieving the aforementioned advantages, the invention isin one aspect directed to a method of producing solid particles of fatfor blending with dry ingredients in a mixing chamber. A fine,downwardly directed spray of atomized liquid fat is introduced into theupper portion of a conventional feed mixing chamber, while a pluralityof fine jets of cryogenic liquid are directed against the downward sprayof liquid fat droplets, so as to cause rapid conversion of the dropletsto solid particles, which then fall into the dry ingredients at thebottom of the mixing chamber. Because of their relative inertness andsafety, liquid nitrogen or carbon dioxide may be used as the chillingagents.

The invention is in another aspect an apparatus for producing solidparticles of fat for blending with dry ingredients in a mixing chamber,comprising means disposed in the upper plenum of the mixing chamberoperable to produce a downwardly directed spray of atomized liquid fatand means for producing a radially inwardly-directed spray of liquidnitrogen or carbon dioxide to surround and impinge against thedownwardly directed spray of liquid fat droplets.

In drawings which illustrate embodiments of the invention:

FIG. 1 is a schematic representation of a feed blender equipped withapparatus according to a preferred embodiment of the invention;

FIG. 2 is a vertical cross-sectional view of the atomizing nozzle, sprayring and cylindrical housing of a cryogenic crystallization apparatusaccording to the embodiment illustrated in FIG. 1;

FIG. 3 schematically illustrates an alternative installation ofapparatus according to the invention in a feed mixing blender.

With reference to FIGS. 1 and 2, one or a plurality of cryogeniccrystallization units according to the invention are housed incylindrical shrouds 10 which open downwardly into the top of aconventional feed mixing chamber 14 equipped with a power drivenblending auger 16. Associated with each cylindrical housing is atop-mounted atomizing nozzle, indicated generally at 18 in FIG. 2,operable to break up liquid fat sprayed therethrough into very smallparticles or droplets. Known such atomizing nozzles include an inletthrough which liquid fat may be introduced (arrow A) and a separatechannel for the introduction of air under pressure (arrow B). To obtainvery fine atomization of the liquid fat, the simultaneous introductionof liquid fat and pressurized air through a known nozzle structuretaking advantage of the Venturi principle must be used. Commerciallyavailable Venturi nozzles found to be useful in applying the presentinvention include 1/8J, 1/4J, 1/2J, and 1J sizes. However, if coarserfat particles are desired, nozzles using no air and liquid fat pressurealone may be employed.

The outer contour of the downwardly directed spray of liquid fatdroplets issuing from the tip 18a of nozzle 18 is indicated by arrows C.The external sources of liquid fat under pressure and of pressurized airare not shown in the drawings, nor is the conventional valve means inthe lines to control the fat and the air. A pair of Jamesbury ballvalves are suitable for controlling the flows of liquid fat, air andnitrogen.

The atomized droplets of fat are sprayed with a cryogenic liquidintroduced through a spray ring 20. The ring may be made of aluminumtubing, stainless steel or copper "K" of a diameter from 1/4| to 3/4|.The diameter of the ring itself will typically be between 6 and 8inches, although the chosen size will vary to suit the mixing systemdesigned for. The inner surface of the toroidal spray ring is drilledaround its circumference with an evenly spaced plurality of small holes22, the number and sizes of which will be chosen according to the flowrates of fat being sprayed.

It is important that holes 22 be drilled equidistant from each otheraround the circumference and have bores biased at an inward angle alongthe bottom of the spray ring, so as to produce an inverted conical spraypattern (arrows D) which converges downwardly and impinges on the streamC of atomized liquid fat droplets.

The cylindrical housing or shroud 10 functions to provide a surface onwhich to mount spray ring 20 and nozzle 18, but also to concentrate andcontain the cold nitrogen or carbon dioxide in the vicinity of theatomized fat. Typically, the dimensions of the shroud will be of theorder of 16 inches diameter and 1 to 5 feet tall, varying according tothe specific application.

Optionally, two heating elements may be included in the apparatus. Thefirst heater, 24, is an element which wraps around nozzle 18 to preventthe fat injected therethrough from solidifying within the nozzle. Theamount of heat may be regulated and controlled by a voltage controller(not shown).

The second heater consists of a standard heat wrap surrounding theshroud (not shown) to prevent any solidified fat from building up on thesides of the shroud. At the end of a day's operation, this second heatersurrounding the shroud may be turned on for a few minutes to melt anysolidified fat which has incidentally accumulated on the interiorsurface of the shroud.

Although the presence of a shroud (housing) for the nozzle/spray ringcombination is desirable for the reasons noted above, the method of theinvention may be carried out by installing an array of nozzles and sprayrings within a mixing chamber 14 directly under the top wall 14athereof, where space limitations so require, as illustrated in FIG. 3.If not already equipped with a vent or exhaust, a blender making use ofthe method and apparatus of the invention should be provided with anexhaust port 26 to vent the nitrogen and air introduced into the mixingchamber.

In operation, blender 14 is first charged with the basic dry ingredientsfor the animal feed or other product which is to be enriched with fat.Liquid fat is then pumped under pressure from a heated storage vesselthrough a pipe to the blender and is sprayed into the mix through asingle or a series of atomizing spray nozzles 18. As noted above, thepurpose of the spray nozzles is to atomize the fat into the smallestpossible particles or droplets.

As the fat is sprayed into the plenum of the blender it is shocked witha spray of liquid nitrogen or carbon dioxide introduced through sprayrings 20. It may also be advantageous in some cases to commence thenitrogen spraying cycle a few seconds before the fat spray cycle iscommenced, to cool down the blender. During spraying of the cryogeniccoolant, the heaters surrounding nozzles 18 are operated to prevent fatfrom freezing within and occluding the nozzles 18.

Crystals of fat similar to snow flakes fall from shrouds 10 into theblender and are uniformly distributed and mixed into the dryingredients. The spraying of fat is stopped when the desired amount ofmaterial has been added and the nitrogen or carbon dioxide flow isstopped simultaneously, along with the heater on the nozzle, marking theconclusion of the mixing cycle. The batch is then emptied from themixer, which is then charged with a new batch for repetition of thecycle.

It will be appreciated that the entire mixing process described abovemay be carried out automatically under the control of a microprocessoroperable to time all stages of the mixing cycle and to actuate valvemeans to control the sprays of liquid fat, air and cryogenic coolant.

EXAMPLE 1

In a system for the production of animal feed, a fat mixture of palm oiland beef tallow was crystallized using liquid nitrogen inside a blender.The fat mixture, having a melting point around 95° F., was heated andstored in the heated vessel at 135° F. The fat was pumped through twelve1/4J nozzles at approximately 40 psig pressure. The nozzles were locatedon the top inner surface of the mixer and arranged in three equidistantrows of four nozzles. Air was provided at 50 psig by compressor.Nitrogen coolant was stored in an 11,000 gallon liquid nitrogen storagevessel and conveyed through a 1" diameter vacuum jacketed pipeline to aseries of spray rings located directly below each nozzle.

At the start of the mixing cycle, 1,600 pounds of dry ingredients,chiefly whey powder, were dumped into the mixture. Fat, air, andnitrogen were sprayed simultaneously through the nozzles for a period of2.5 minutes, over the course of which approximately 400 lbs. of fat intotal was sprayed. The percentage of fat in the final mix is determinedby the selected amount of time that the fat, air and nitrogen aresprayed at a given pressure.

The mixture was then emptied and the batch of product was bagged.Samples of the mixture of crystallized fat and whey powder resembled afine flour. Fineness of the mix can be enhanced by increasing the amountof nitrogen and/or increasing the air pressure.

EXAMPLE 2

In the preparation of an enriched bakery product, vegetable oil wascrystallized outside the blender and subsequently added to flour.

Vegetable oil in the form of solid 20 lb. blocks (melting pointapproximately 75° F.) was placed in a heated vat at approximately 110°F. The melted oil was then pumped out of the vat and through anozzle/spray ring/shroud arrangement as described in connection withFIGS. 1 and 2. The fat was not sprayed into a blender, however, butdirectly into a drum located beneath the shroud, for approximately 10minutes. About 40 lbs. of crystallized oil was thereby collected anddumped into a mixer containing a desired proportion of flour. Theentirety was mixed and the product batch was bagged. Sampling of themixture showed the powder to be dry and free of lumps.

Those skilled in the art will recognize that the principles of thepresent invention will afford a number of applications, which have onlybeen exemplified herein. Accordingly, the scope of the invention isdefined by reference to the appended claims.

I claim:
 1. A method of producing solid particles of fat for blendingwith dry ingredients in a mixing chamber, comprising introducing a fine,downwardly directed spray of atomized liquid fat into the upper portionof the mixing chamber while directing a plurality of fine jets ofcryogenic liquid against the downward spray of liquid fat droplets so asto cause rapid conversion thereof to solid particles which fall into thedry ingredients at the bottom of the mixing chamber.
 2. A methodaccording to claim 1, wherein said cryogenic liquid is nitrogen.
 3. Amethod according to claim 1, wherein said cryogenic liquid is carbondioxide.
 4. A method according to claim 1, wherein said fine jets ofcryogenic liquid are regularly dispersed in circular symmetry about thespray of atomized liquid fat and directed obliquely inwardly against theliquid fat droplets.
 5. Apparatus for producing solid particles of fatfor blending with dry ingredients in a mixing chamber, comprising:(a)means disposed in the upper plenum of said mixing chamber operable toproduce a downwardly directed spray of atomized liquid fat; and (b)means for producing a radially inwardly-directed spray of liquidnitrogen or carbon dioxide to surround and impinge against thedownwardly directed spray of liquid fat droplets.
 6. Apparatus accordingto claim 5, wherein said means operable to produce a spray of liquid fatcomprises an atomizing nozzle in communication with an external sourceof liquid fat under pressure, and first valve means for controlling therate of spraying of liquid fat through said atomizing nozzle. 7.Apparatus for producing solid particles of fat for blending with dryingredients in a mixing chamber, comprising:(a) means disposed in theupper plenum of said mixing chamber operable to produce a downwardlydirected spray of atomized liquid fat comprising an atomizing nozzle incommunication with an external source of liquid fat under pressure, andthe first valve means for controlling the rate of spraying of liquid fatthrough said atomizing nozzle; and (b) means for producing a radiallyinwardly-directed spray of liquid nitrogen or carbon dioxide to surroundand impinge against the downwardly directed spray of liquid fatdroplets, wherein the radially inwardly-directed spray of liquidnitrogen or carbon dioxide comprises:(i) a tubular spray ringsurrounding the downward spray from said nozzle and presenting along thebottom thereof a plurality of regularly spaced spray holes, said holesbeing angled inwardly to direct liquid nitrogen or carbon dioxideintroduced under pressure into said spray ring in a conical spraypattern converging on the stream of atomized liquid fat droplets; (ii)an external source of pressurized liquid nitrogen or carbon dioxide;and(iii) second valve means interposed between said source of liquidnitrogen or carbon dioxide and said spray ring, operable to control thespray of liquid nitrogen or carbon dioxide through said spray ring. 8.Apparatus according to claim 7, wherein said atomizer nozzle and saidtubular spray ring are enclosed within and disposed at the top of acylindrical housing opening downwardly into the top of said mixingchamber.
 9. Apparatus for blending liquid fat with dry animal feed toproduce a free-flowing mix, comprising:(a) a mixing chamber equippedwith means for stirring feed mix and added particles of fat together;(b) a plurality of cylindrical housings distributed along the top ofsaid chamber, each having a bottom opening communicating with theinterior of said chamber; (c) an atomizing nozzle disposed within eachof said cylindrical housings in the upper portion thereof, adapted todirect a downardly directed spray of atomized liquid fat particles intothe top of its cylindrical housing when operably connected to acontrolled external source of liquid fat and air under pressure; and (d)a tubular spray ring mounted within each of said cylindrical housingsand configured to surround the donward spray of liquid fat droplets fromthe atomizing nozzle disposed therein with an inverted spray pattern ofcryogenic liquid converging on the downward spray of liquid fat dropletsfrom said atomizing nozzle, when said spray ring is operably connectedwith a controlled external source of pressurized cryogenic liquid.